I had heard once that it is better to leave a computer on for four hours than turn it off and then back on as it is less wearing to leave it on that amount of time than cycle it through the on and offs - is there something similar for tube amps? An amount of time better to leave it idel instead of turning it off and then on again, besides in Iowa it helps warm the home in the winter.

Here's my observations over my life of tube amp listening and tending (which started as a boy with my father's Dynaco preamp, amp and tuner):

* Playing music through a healthy tube amp over the course of a day and longer is a good thing sonically, it sounds better and better as the day progresses. There's nothing like a tube amp all heated up and controlling the speakers.

* It's always less of a stress on output tubes to have music flowing through them as opposed to being turned on with no signal passing through. Output tubes last longer that way.

* I confess I've done this more than once, but leaving tube amps powered up when no one is about is. . . not prudent.

Here is what I do....In the evening I would turn the amp on a half hour before I was going to listen, leave in on until I was going to bed. That would be the normal, Monday through Friday.

On weekends, if I was going to listen in the morning I would turn it on and listen, and if I knew it was not going to be until late that evening, that I would listen again, I would turn it off. If I might listen sporadicly throughout the day, I would leave it on.

With that said, I had Steve's ZLSA line stage which I didn't turn off for almost three years!

With the Torii-I it heats up much faster than any of Steve's other amps, it doesn't take hours for it to sound its best, but I would still and try to today, not turn it on and off several times during the day.

It is a bit of an urban legend that normal receiving type tubes can be killed by power cycling. What generally does kill them are hours powered up, leading to eventual outgassing or lack of cathode emission. So if you wish to spare your expensive NOS tubes as much as possible, then you power your amps on when you want to use them, and off again when you don't.

The confusion may stem from the fact that some high power transmitting tubes, which uses exceptionally large cathodes, does have specs for maximum starting current on power on. This is particular true for tubes employing directly heated Thoriated Tungsten filaments, where the difference between filament cold- and hot resistance is significantly higher than in the more common indirectly heated tubes.

One data point I found what that of the original WW-II era EINAC computer, which used roughly 18'000 tubes. The operators found that if they power cycled the machine every day, then they would have a tube fail due to an open filament roughly every 2-4 days, leading to downtime while they located the problem. In their case they eventually did decide to just leave the machine on, though at an atrocious cost in the form of the power consumed. EINAC used ordinary receiving type tubes, like 6SN7GTs and 6L6Gs.

If we take their data and run with them, then we can expect a tube failure roughly every 36'000 power cycles or so, or about 25 years for one tube, if we power cycle it four times a day.

Also note that back in the day having tubes in radios and TVs fail due to an open filament was a fairly rare event, compare to other failure modes. I keep a box with my 'dead' tubes that I locate when restoring vintage radios and whatnot, and I am almost positive I don't have a single receiving type tube with an open filament. Gas, low peak emission, low transconductance or heater/cathode shorts are the common problems. The box currently contains about a dozen or two of dead tubes, for those who are wondering.

So for a class A amplifier output tube we can prolong the lifetime on - in particular - the cathode by running it as little as possible.

Also note that having tubes running with only filament power applied and no HT, as is possible in some Hi-Fi amps, is *exceptionally* bad for the cathodes. Doing this leads to a problem known as 'cathode poisoning', which was called 'interface' back in the day. You just don't want to do this, no matter what some audiophiles say.

Whether there are any sonical benefits from leaving your amps powered up for hours before you want to listen to them, is a different question altogether, of course.

It really isn't complicated, even if I managed to make it sound that way:

Do:

*) Run your tubes as cool as possible - but no cooler. High temperatures reduces longevity, but if class A they must survive, then so be it. A tube last a certain amount of hours at a particular power level, and it will be the same whether you burn them up all at once, or in piecemeal fashion, one hour at a time.*) Use a step start circuit in your amps if you feel generous. But it isn't really needed as far as the tube heaters are concerned. Exception: Very large transmitter tubes, which we usually don't find in audio amps.

Don't:

*) Worry about power cycles, they don't detract from the lifetime of your tubes in any meaningful way. Just switch on and off when you want to use your audio equipment.*) Run your tubes with zero cathode current either, IE. 'standby mode' with only heater power applied. This also kills the cathodes eventually, and it does in particular not prolong the lifetime of tubes compared to just turning them on and off when required. Standby mode is just a waste of power and tube life.

i hope it isn't considered a "tweak", steve, but cryo treating most metals enables them to do their jobs better and longer. the data suggest that cryo treated tools, in the case of saw blades, guns and hand tools, among others, provides a longer, more effective service life. in the case of vacuum tubes, to my ear, the sound is better. as a result tubes are cheaper and expense is less of an issue. there are oodles of us out here that believe this to be the case and would deny this process to be a "tweak" don pettit, long beach, washington

The issue with cryo treating tubes is that if it does increase longevity, then why wasn't this discovered and employed by the tube gurus at RCA and the other major tube laboratories around the world? Considering the extreme level of detail and trouble they went through in order to increase the lifetime of their military and long life commercial offerings, then I'd suspect a dip in liquid Nitrogen wouldn't be beyond them if it helped.

The transmitter tubes in NASA's Voyager I and II space probes were not cryo treated, and yet they are still going strong today, almost 40 years after they were manufactured.

You can read (a lot) more about tube manufacturing and quality control in the book 'Electron Tube Design', published by RCA in 1963. It is available as a free download, all 943 pages of it, from this page.

right frank, so why are some major manufacturers and users of cryo treated implements using the process seeing increased service life and effectiveness of a wide range of metal tools, etc. regardless of what a book written in 1963 states? the process is not a "dip". it is a computer controlled process that consists of a slow ramp down, 24 hour holding at a precise temperature dictated by the metal and the result desired, and a slow ramp up to room temperature. computers that could do this were to come into being a long time later and then the process had to be refined. the book about tubes could be likened to newton's observations about physics, don't you think? much more is known now than when isaac tossed the apple upward. for a little more info on this see website cryo plus.com. these companies would not be paying these fees if they were not seeing results and then consult my ears. there is just plain ,more there, musicwise. don

also, frank, consult ron sheldon at cryoset. he sells tubes around the world to people like me who like to waste their money and see shorter tube life. and they are all convenced that the music sounds inferior. don

Nice, Don, maybe you should read what I actually wrote, instead of commenting on what I didn't?

*) There is no doubt cryo treatment - along with other temperature treatments of many metals and alloys - can change their mechanical properties, and thus for instance increase wear resistance, bulk resistivity and other physical properties. This is a well established technique by now.

*) However there is no mechanical wear on a tube in service, unless you hit it with a hammer. A tube wears out due to - among other things - chemical exhaustion of the cathode, contamination of the cathode due to migration of impurities from the cathode sleeve (usually made from a very pure nickle alloy to try and prevent this from happening), and slow outgassing from the metals and the glass making up the tube. Sometimes you have slow leaks at the seals as well. It is not clear to me how improving the mechanical qualities of the bulk metal making up the tube structure can prevent these processes from happening, or slow them.

*) Tubes have been space rated since the late fifties. I would be extremely surprised if part of that certification of different tube types didn't incorporate some form of extended storage at cryogenic temperatures a bit above the absolute zero. The intention being to see what would happen when a satellite transmitter is powered up again after a prolonged break from service. Age tests would be the logical extension to see how the abuse might have influenced the useful service life of space rated tubes. I have never heard of any such effect being observed. Please give any references if you know of any such studies which did see it, involving the usual 5 to 10 thousand tubes.

*) What you describe as a cryo treatment is really a 'dip' by modern standards, considering the testing modern, high power tube equipment is subject to as a matter of course when being man/life rated. The (N)MRI scanner at your local hospital is likely to still contain quite a few serious power triodes, probably made by these guys. Being able to, say, double the time between scheduled tube replacements in those settings would be a big deal if something as simple as cryo treatment works. You could really make a killing in that industry with an effect like this.

*) I would be highly surprised if an effect like you describe, an unknown mechanism extending the lifetime of low power vacuum devices via cryo treatment, exists, and at the same time hadn't accidentally been discovered by half the physics departments of every reasonable university in the world. Those places use liquid Nitrogen by the truckload, literally, and not (only...) to cool their beer.

*) I didn't say anything about how such a treatment might influence the sound of a tube. But since you did, please allow me to comment. Did it occur to you that we are actually not listening to the metal of the tube, but to the structure of the vacuum in between it?

*) It is for you to decide whether you waste your money on any service you buy, not something I can nor will comment on. Please leave the ad hominem attacks at the door if you wish for us to continue this conversation.

to each his own. you seem convinced. i am convinced. ron sheldon is convinced. many others are convinced. tubes are full of gas and perhaps i am too. or perhaps others are. no ad hominem there, is there? don pettit, long beach, washington

May I add my 2 cents on cryo. A little background on me first. I am a Sr. Manufacturing Engineer specializing in cutting tools for a very large manfactuer of big YELLOW equipment.I have personally conducted extensve tests on cryo treatment on cutting tools and IT DON'T WORK. Snake oil folks.Freezing your tubes? I can't imagine it matters a bit. But the main thing to remember is I don't know shit about how music comes out of the boxes setting on my floor. Any technology I don't understand must be magic.